Digital Television Dr Nikos Desypris ndessipris yahoo com Nov

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Digital Television Dr. Nikos Desypris ndessipris@yahoo. com Nov. 2017 Postgraduate course University of Athens

th 5 Lecture on Digital TV DTV Transmission and Reception System DTV Transmission Systems

DTV worldwide system standards

Aspect Ratio comparisons

Popular DTV systems Name lines / pictures/ Scanning picture second lines/pictur Aspect e (active) Ratio HDTV 750 60 60 fields/sec – progressive 720 p HDTV 1125 30 60 fields/sec – interlaced 1080 i SDTV 640 60 60 fields/sec – interlaced 480 Other digital TV standards EDTV 640 60 60 fields/sec – interlaced 480 LDTV 320 60 60 fields/sec – interlaced 16: 9 240 Roughly 4 SDTV channels -> 1 HDTV channel (720 p)

Interactive Services The digital programming platform Structure of middleware ØResources ØMiddleware ØAPI üAudio and video streams üCommands or events üRecords and files üH/w resources ØApplications (interactive services)

Interactive Services

Interactive Services Interactivity through the set-top box

Interactive Services Two types of interactivity Local interactivity Provision of an interactive channel through out the broadcasting network

Interactive Services Electronic programming guide (EPG) Enhanced TV (interaction of the user with the station though the digital television set itself!) Individualised TV (level of interactivity similar to that of a DVD player: set cameras, sound and subtitles at will) Internet TV (accessing internet on TV) Video on Demand (Vo. D) (different to EPG: the user searches a database of films, sees when they are on, when and on which channel) Commercials (similar application to shopping channels – not in Greece) Purchase of MP 3 files, films or educational products to be downloaded from the supplier after purchase

Interactive Services Other services Monoprogramming: showing of one program on an exclusively designated frequency (often used for the transmission of HDTV) Multiprogramming: many programs on an exclusively designated frequency (between 4 and 6 SDTV channels on one frequency) Mobility, portability: reception of television signals in different movement conditions on TV sets on vehicles or TV receivers integrated in cell phones or palmtops. Multiservices: several broadcasting and telecom services simultaneously on the same digital TV platform.

Interactive Services

Interactive Services Return channel: Ø South Korea: ADSL technology Ø Finland: Shared land telephone system Ø Italy: Shared land telephone system Ø Japan: ADSL technology Ø Recommended return channel in Brasil: using IEEE Wi. Max technology Note in the UK the return channel never reached the critical number of households for successful commercial exploitation

Standard options for DTV (broadcast) Five DTV systems worldwide: 1. American Advanced television Systems Committee (ATSC) 2. European Digital Video Broadcasting Terrestrial (DVB-T) 3. Japanese Integrated Services Digital Broadcasting Terrestrial (ISDB-T) 4. Brazilian International Standard for Digital Television (ISDTV or ISDTV-Tb) 5. Chinese Standard for Digital Television (DTMB) Note: Two standards exist for hand held devices: Ø Digital Video Broadcasting Handsets (DTV-H) and Ø Digital Multimedia broadcasting (DMB), with twice the transmission rate of DTV-H

Standard options for DTV (broadcast) System similarities: They are using the same frequency band Improve vertical and horizontal resolutions Present an aspect ratio of 16: 9 Support multichannel sound Support data transmission Main difference is the modulation technique used to broadcast the signal: Single carrier modulation Multiple carrier modulation

Standard options for DTV (broadcast)

Standard options for DTV (broadcast) Transmission standards: 8 -VSB: 8 level Vestigial Sideband COFDM: Coded Orthogonal Frequency Division Multiplexing QFDM: Quadrature Frequency Division Multiplexing PSK: Phase Shift Keying QPSK: Quadrature Phase Shift Keying

Standard options for DTV (broadcast) Broacast standard, Country: Middleware standards Ø ATSC, US: DASE – DTV applications software environment Ø ISDB-T, Japan: ARIB – Association of Radio Industries and Business Ø ISDTV, Brasil: Ginga Ø DVB-T, Europe: MHP – Multimedia Home Platform Ø DTMB, China: IMP – Interactive Media Platform

Standard options for DVB-T (Europe)

Standard options for DVB (Europe) DVB is a suite of international standards led mainly in Europe Are maintained by the DVB project, an international industry consortium with more than 270 members Are published by a Joint Technical Committee (JTC) of the European Telecommunications Standards Institute (ETSI), European Committee for Electrotechnical Standardization (CENELEC) and European Broadcasting Union (EBU).

Standard options for DVB-T (Europe) LMDS: Local Multipoint Distribution System MMDS: Multichannel Multipoint Distribution System

Standard options for DVB-T (Europe)

Standard options for ATSC (US)

Standard options for DVB-T (Europe)

Standard options for ISDB-T (Japan)

Standard options for ISDTV (Brasil)

Standard options for DTMB (Chinese)

Standard options for DTV (broadcast) Global adoption of DTV standards

DTV Transmission & Reception System Ø Layered approach to system design Ø Broadcasting system: includes four subsystems: Presentation / Compression / Transport – Multiplex / Transmission Ø Distribution channels: Traditional: Terrestrial / Cable / Sattellite New: Internet TV / IPTV / Hand-held devices Ø DTV receiver: the broadcast sequence is reversed Reception / Transport – Demultiplex / Decoding / Presentation

Layered approach to system design

Broadcasting system: 4 sub-systems Ø Presentation: ü image format and sound Ø Compression: ü reduces data rate to practical levels Ø Transport multiplex: ü packetizes audio, video and data: ü includes assembly instruction for the DTV receiver Ø Transmission: ü adds error correction and modulates symbols for channel distribution

The DTV Receiver: 4 sub-systems The sequence is reversed Ø Reception: ü Signal capture, ü demodulation and ü recovery of data packets from the transmission channel Ø Transport demultiplex: ü extraction of audio, ü video and data packets and ü assembly instructions Ø Decoding: ü Expansion of compressed audio and video data Ø Presentation: ü audio and video are synchronised and ü the complete program is ready for viewing

Layered approach to system design

Engineering Basics Ø Voltage levels Ø Noise Ø Units of data ü Bits, Bytes and Words Ø Repetive signals: frequency and the Hertz Ø Analogue to Digital Conversion and Quantisation Ø Data Structure and Processing ü Packets, Headers and Payloads; Streams; Data Buffer and Parsing

Engineering Basics Ø Voltage levels For digital systems, discrete voltage level represent information. Two levels are used for 0 and 1; however 3, 4 or more distinct levels can be used Ø Noise Can be internal or caused from external sources. Becomes a problem if amplified Ø Units of data bit: 0 or 1 byte: 8 bits, 256 levels word: two bytes, 16 bits, 65536 values double word: four bytes, 32 bits, 232 values in digital audio applications: 18 and 20 bits words in digital video applications: 10 and 12 bit words are common

Engineering Basics Ø Repetition signals: the notion of the frequency Unit: one cycle per sec referred as Hertz named after the German physicist Heinrich Rudolf Hertz (1857 -1894) Definition of 1 Hz, 1 KHz, 1 MHz, 1 GHz Audio signals are between 20 Hz and 20 KHz. Video images have spatial (within a frame) and temporal (between successive frames) frequency characteristics

Engineering Basics Analogue to Digital Conversion and Quantisation

Engineering Basics Data Structure and Processing Bits and bytes are arranged in groups referred as data structures or object model, which are processed by machines üPackets, Headers and Payloads Data is grouped into packets having the actual content of transmission (the payload) and additional header information describing the payload üStreams Continuous transmission of data (data stream): can be asynchronous (at random), synchronous (with a defined timing) or isochronous (defined amount of data over a time period) üData Buffer A storage device, often RAM that stores and transmits data at different rates. üParsing Examining a data stream for defined values in a data structure and extracting desired information is called parsing

Broadcasting system: 4 sub-systems Ø 1. Presentation: ü image format and sound Ø 2. Compression: ü reduces data rate to practical levels Ø 3. Transport multiplex: ü packetizes audio, video and data: ü includes assembly instruction for the DTV receiver Ø 4. Transmission: ü adds error correction and modulates symbols for channel distribution

Broadcasting System 1: Presentation Ø General Ø Visual Perception: ü Luminance sensitivity, ü Colour Sensitivity Ø Video Presentation formats: ü ü ü ü Aspect Ratio Scanning methods Refresh Rate Resolution and pixel grid Synchronisation Pixel Squareness Sampling and colorimetry Ø Audio Formats: ü Audio Perception ü Audio Presentation Formats

Broadcasting System 1: Presentation Ø General Ø Visual Perception Ø Video Presentation formats Ø Audio Formats

Broadcasting System 1: Presentation General Ø Presentation is about Immersive consumption; Ø HDTV was envisaged as a large-screen theatrical viewing experience Ø Importance of surround sound in the immersive experience DTV is a mass product at an affordable price based on current technological limits

Broadcasting System 1: Presentation Ø General Ø Visual Perception Ø Video Presentation formats Ø Audio Formats

Broadcasting System 1: Presentation Ø Visual Perception ü General ü Luminance sensitivity, ü Colour Sensitivity

Broadcasting System 1: Presentation Ø Visual Perception ü General 107 66 43 cm 54 33 22 cm 160 99 65 cm

Broadcasting System 1: Presentation Ø Visual Perception ü Luminance sensitivity Y= 0, 30 * Red + 0, 59 * Green + 0, 11 * Blue ü Colour Sensitivity Combinatorial process of mixing red, green and blue Visible light is between 380 nm and 760 nm Red -> 440 nm Green -> 540 nm Blue -> 700 nm

Broadcasting System 1: Presentation Ø General Ø Visual Perception Ø Video Presentation formats Ø Audio Formats

Broadcasting System 1: Presentation Ø Video Presentation formats: ü General ü Aspect Ratio ü Scanning methods ü Refresh Rate ü Resolution and pixel grid ü Synchronisation ü Pixel Squareness ü Sampling and colorimetry

Broadcasting System 1: Presentation Ø Video Presentation formats: General A video format consists of : - Aspect ratio - Raster (pixel grid structure) - Scanning method - Refresh rate Note: Analogue TV had only one video format and one colour space sampling structure. There are 18 different DTV formats in the ATSC standard (many more in satellite and cable!)

Broadcasting System 1: Presentation Ø Video Presentation formats: Aspect Ratio

Broadcasting System 1: Presentation Ø Video Presentation formats: Scanning methods

Broadcasting System 1: Presentation Ø Video Presentation formats: Refresh Rate Ø Movie industry 24 frames/sec Ø TV: 30 Hz (half the AC 60 Hz power line frequency) Ø Other frame rates: 29. 97, 30, 60, 59. 94 Ø Film rates: 24 or 23. 98

Broadcasting System 1: Presentation Ø Video Presentation formats: Resolution and pixel grid Ø Always defined as pixels per line by pixels per frame Ø Refresh rate defines the number of complete frames; ü 60 p: 60 progressive frames per second ü 60 i: denotes 30 frames per second, each frame comprising of two interlaced fields (one field odd lines, the other even lines) Important note: The no of pixels and lines in an image format is not a statement of the image resolution which is dependent on the entire signal processing chain

Broadcasting System 1: Presentation Ø Video Presentation formats: Synchronisation The timing relationship of the scanning process that produces pixels, lines and a display raster (pixel grid) must be unambiguously established. 1920 pixels x 1080 lines 1280 pixels x 720 lines Define the active pixels and lines in a display, while the actual scanning number for each video presentation format is 2200 pixels x 1125 lines and 1650 pixels x 750 lines respectively

Broadcasting System 1: Presentation Ø Video Presentation formats: Synchronisation DTV eliminates blanking intervals during compression

Broadcasting System 1: Presentation Ø Video Presentation formats: Pixel Squareness Square pixels are defined (in DTV standards) as when the number of horizontal to vertical pixels is the same proportion as the display aspect ratio. 640: 480 = 4: 3, HD formats 1920 x 1080 and 1280 x 720 are 16: 9, therefore HD formats employ square pixels. However SD, 720 x 480 and 704 x 480 are not 4: 3 and it is quite important for creating graphics on video. A simple solution is to create a graphics canvas that is the same display format as the intended display

Broadcasting System 1: Presentation Ø Video Presentation formats: Sampling

Broadcasting System 1: Presentation Ø Video Presentation formats: Colorimetry

Broadcasting System 1: Presentation Ø General Ø Visual Perception Ø Video Presentation formats Ø Audio Formats

Broadcasting System 1: Presentation Ø Audio Formats: ü Audio Perception ü Audio Presentation Formats

Broadcasting System 1: Presentation Ø Audio Formats: Audio Perception Audible sound for young people: 20 Hz to 20 KHz

Broadcasting System 1: Presentation Ø Audio Formats: Audio Presentation Formats

Broadcasting System 2: Compression Ø MPEG-2 Video Compression ü ü Exploiting Redundant Visual Information Group of Pictures Compression Steps Exploiting Temporal Redundancy Ø Audio Compression ü Aural Perception and Compression Algorithms Ø Masking Ø Framing

Broadcasting System 2: Compression Ø MPEG-2 Video Compression Ø Audio Compression

Broadcasting System 2: Compression Full bandwidth HDTV picture with 6 audio channels is 1, 5 GBps. To fit in a 6 MHz channel, data reduction of 50: 1 for video and 12: 1 for audio are common. Compression generation: an encoding and decoding cycle. Each compression generation creates artefacts Consumer electronics are not to highest fidelity; however they have consumer satisfaction Compression ‘engines’ are divided in two broad categories: Lossless compression reduces the volume of data and, when reconstructed restores it to its original state, perfectly without any loss of information Lossy compression discards data based on auditory and visual sensory characteristics and limits

Broadcasting System 2: Compression Indicative video codecs: VC 1 derived from Windows Media and MPEG-4 Part 10 claim to deliver the same quality of MPEG-2 with half the rate MP 3 is part of MPEG-1 or MPEG-2 Audio Layer III Advanced Audio Coding (AAC) is also an MPEG standard AC-3 (Audio Codec 3) with support of up to 6 channels was intended for theatrical applications Key data JPEG focuses on still images MPEG (Motion Pictures Expert Group) MPEG 1: 1988 -1991 MPEG 2: 1994 MPEG 4, Part 10: latest version of mpeg

Broadcasting System 2: Compression Ø MPEG-2 Video Compression Ø Audio Compression

Broadcasting System 2: Compression MPEG-2 Video Compression ü General ü Exploiting Redundant Visual Information ü Group of Pictures ü Compression Steps ü Exploiting Temporal Redundancy

Broadcasting System 2: Compression MPEG-2 Video Compression: General Compression is characterised by a ratio (video 50: 1, audio 12: 1) The higher the ratio the fewer the number of bits Raw bit rates for HD video are about 1, 5 Gbps. With 4: 2: 2 sampling and 50: 1 compression, yields 30 Mbps. With 4: 2: 0 sampling (1 Gbps) and 50: 1 compression results 20 Mbps. The higher rate (30 Mbps) can survive a generation or two of editing without artefact, while the lower rate (20 Mbps) is used for presentation only. For multiple generations of compression and decompression in production environment, video should be at least 100 Mbps for HD and 40 Mbps for SD.

Broadcasting System 2: Compression MPEG-2 : Exploiting Redundant Visual Information Coding only scene differences results in significant compression, but depends on scene complexity, for example: High: Detail -> spatial complexity: rain grounds Motion: Change -> temporal complexity: sports Low: Still = simple: talking head, stationary text and graphics MPEG-2: two attributes for scene complexity: profile and level: Profile compression complexity related to colour sampling: Simple; Main; 4: 2: 2 , SNR, Spatial and High Level specifies picture size in pixels: Low; Main; High 1440 and High

Broadcasting System 2: Compression MPEG-2 : Exploiting Redundant Visual Information Profile L e v e l SD is MP @ML HD is MP @HL

Broadcasting System 2: Compression MPEG-2 Video Compression: Group of Pictures Ø I frames: Intraframe, encoded independent of other frames Ø P frames: Predictive, encoding is dependent on Ø B frames: Bidirectional, encoding is dependent on previous or subsequent I or P frames Ø A ‘long GOP’ is usually up to 15 frames such as: I B B P B B, corresponding to 0, 5 sec on 1080 i at 30 Hz, or 0, 25 sec for 720 p at 60 Hz (important for switching TV channels) Ø I frames are called anchor frames

Broadcasting System 2: Compression

Broadcasting System 2: Compression MPEG-2 Video Compression: Compression Steps Compression of an I-frame: ü It is divided into 8 x 8 pixels blocks ü Discrete cosine transform (from 8 bits pixels to 11 bits coefficients!) ü Weighting and Requantisation (to reduce high frequency coeffs) ü Variable length coding (to assign small codewords to most common symbols as in Morse code where E, T ->. and _) ü Run length coding (to code a sequence of same digits more efficiently)

Broadcasting System 2: Compression MPEG-2 Video Compression: Exploiting Temporal Redundancy I frame – current frame = P Frame (different pixels not values!) frame 2 – I frame – P frame = B frame

Broadcasting System 2: Compression

Broadcasting System 2: Compression P: difference 1 and 3 B: difference 2, I and P> P>B

Broadcasting System 2: Compression Ø MPEG-2 Video Compression Ø Audio Compression

Broadcasting System 2: Compression Ø Audio Compression ü Aural Perception and Compression Algorithms, based on psychoacoustic model • Masking: When one sound hides another sound, it need not be encoded • Framing: Further data reduction is taking place by requantising high frequencies using the psychoacoustic model

Broadcasting System 3: Transport Multiplex Ø Compressed Data Streams Ø Packetised Transport ü Multiplex Concepts ü PSI and Program Assembly v Transport Stream Multiplex v Statistical Multiplexing and Rate Shaping

Broadcasting System 3: Transport Multiplex Ø Compressed Data Streams Ø Packetised Transport

Broadcasting System 3: Transport Multiplex Ø Compressed Data Streams The result of compression process is a continuous flow of audio and video data known as an Elementary Stream (ES) ES become part of Packetized Elementary Streams for not loosing audio/video timing relationship

Broadcasting System 3: Transport Multiplex Ø Compressed Data Streams Ø Packetised Transport

Broadcasting System 3: Transport Multiplex Ø Packetized Transport Two types of MPEG streams: Program and Transport Program streams: üare used in environments that rarely corrupt data (such as a DVD player) and ücontain a single audio and video program Transport streams: üEnable robust delivery of data over noisy channels and error prone environments ümay contain numerous programs üpackets are much smaller that those in program streams (only 188 bytes)

Broadcasting System 3: Transport Multiplex Packetized Transport: Multiplex concepts

Broadcasting System 3: Transport Multiplex Packetized Transport: Program Specific Information (PSI) enables Program Assembly

Broadcasting System 3: Transport Multiplex Packetized Transport: Transport Stream Mulitplex ASI: Asynchronus Serial Interface

Broadcasting System 3: Transport Multiplex Packetized Transport: Statistical Multiplexing & Rate Shaping

Broadcasting System 4: Transmission Ø Data Protection ü ü Randomisation Reed Solomon Encoding Data Interleaving Trellis Encoding Ø Digital Modulation ü Modulation v v v Analogue Modulation Digital Modulation Vestigial Side. Band Modulation (VSB) Quadrature Amplitude Modulation (QAM) Quartenary Phase Shift Keying (QPSK)

Broadcasting System 4: Transmission Ø Data Protection ü Randomisation: § Spreads data over the full transmission channel § Scrambling the stream avoiding repetitive patterns ü Reed Solomon Encoding § Use of forward error Correction Code for correcting multiple bit errors, since retransmission is not possible ü Data Interleaving § Spreading data over time in order to avoid lost sequences due to impulse noise (i. e. lightning) ü Trellis Encoding § Transforming bits to symbols used to modulate the RF carrier (generally depends on the modulation standard)

Broadcasting System 4: Transmission

Broadcasting System : Summary Ø Four sub-systems form a DTV broadcasting system: Presentation, compression, transport and transmission Ø Exploitation of the characteristics and limitations of the sensory perception are used in DTV presentation and compression systems Ø Packetized audio and video, along with assembly instructions are sent to a DTV receiver Ø Digital transmission uses sophisticated method of error protection and correction

The DTV Receiver: 4 sub-systems The sequence is reversed Ø Reception: ü Signal capture, ü demodulation and ü recovery of data packets from the transmission channel Ø Transport Demultiplex: ü extraction of audio, ü video and data packets and ü assembly instructions Ø Decoding: ü Expansion of compressed audio and video data Ø Presentation: ü audio and video are synchronised and ü the complete program is ready for viewing

The DTV Receiver: 4 sub-systems

The DTV Receiver: 4 sub-systems Ø Reception Ø Transport Demultiplex Ø Decoding Ø Presentation

DTV Receiver System 1: Reception & Demodulation Ø Reception: ü Signal capture, ü demodulation and ü recovery of data packets from the transmission channel

The DTV Receiver: 4 sub-systems Ø Reception Ø Transport Demultiplex Ø Decoding Ø Presentation

DTV Receiver System 2: Transport Stream Demultiplexing Ø Transport demultiplex: ü extraction of audio, ü video and data packets and ü assembly instructions

The DTV Receiver: 4 sub-systems Ø Reception Ø Transport Demultiplex Ø Decoding Ø Presentation

DTV Receiver System 3: Decoding Ø Decoding: ü Expansion of compressed audio and video data

The DTV Receiver: 4 sub-systems Ø Reception Ø Transport Demultiplex Ø Decoding Ø Presentation

DTV Receiver System 4: Program Assembly & Presentation Ø Presentation: ü audio and video are synchronised and ü the complete program is ready for viewing

DTV Receiver Issues Ø Reception and Error Correction: ü The Cliff Effect ü Multipath Reception Ø Audio/Video Synchronization Ø Presentation Concerns ü ü Display Native Resolution Scanning and Frame Rate Conversion Aspect Ratio Interoperability Display Colour Primaries

DTV Receiver Issues

Emerging Technologies and Standards Ø Presentation ü Beyond 1080 60 p Ø Compression ü ü MPEG-4 VC-1 MPEG-7 MPEG-21

Emerging Technologies and Standards Presentation : Beyond 1080 60 p

Emerging Technologies and Standards Ø Compression ü MPEG-4 ü MPEG-7 ü MPEG-21

LED and LCD Television Receivers LCD displays (depends on the source of light positioned behind the screen) LED displays (or plasma displays: emit light directly from LEDs) LED-backlit LCD TVs (the light behind the screen is LED) LED-backlit LCD TVs differ from conventional CCFL-backlit LCD TVs in the following: Ø Produce images with greater dynamic contrast. Ø With Edge-LED lighting they can be extremely slim. Models on the market can be approximately one inch thick. Ø Offer a wider color gamut, especially when RGB-LED backlighting is used. Ø Less environmental pollution on disposal. Ø Higher price. Ø Generally 20 -30% lower power consumption ref: www. wikipedia. org